I have never found a record that lists them as brothers. However in the Luxroots data I have found the following:
Petrus EngelmanBorn: February 3, 1856 in Hosingen (Luxembourg) Parents listed as Urban Engelman, 23 and Anna Maria Catharina Koch, 26.
Dominique EngelmannBorn: April 8, 1859 in Hosingen (Luxembourg) Parents listed as Urban Engelman, 26 and Maria Catharina Koeth, 28.
Catharina EngelmannBorn: October 11, 1864 in Hosingen (Luxembourg) Parents listed as Urbain Engelmann, 33 and Catharina Koch, 36.
While not a perfect match (is Koeth=Koch?) I believe these three records all refer to the same parents. Furthermore the death records for Peter Engelman and Margaret Peake confirm the parents names (closer on Margarets then Peters).
Thanks for the offer to send a copy of the photo, but I really don't know what I would do with it.
Very sorry to hear about the Hall family. That is a very sad situation. I hope she at least took some comfort in her daughters birth.
By the way, most of my data (besides the Luxroots data) comes from this website: